Abstract
Aflatoxins (AFs) are a group of carcinogenic and immunosuppressive mycotoxins that threaten global food safety. Globally, over 4.5 billion people are exposed to unmonitored levels of AFs. Aspergillus flavus is the major source of AF contamination in agricultural crops. One approach to reduce levels of AFs in agricultural commodities is to apply a non-aflatoxigenic competitor, e.g., Afla-Guard, to crop fields. In this study, we demonstrate that the food fermenting Aspergillus oryzae M2040 strain, isolated from Korean Meju (a brick of dry-fermented soybeans), can inhibit aflatoxin B1 (AFB1) production and proliferation of toxigenic A. flavus in lab culture conditions and peanuts. In peanuts, 1% inoculation level of A. oryzae M2040 could effectively displace the toxigenic A. flavus and inhibit AFB1 production. Moreover, cell-free culture filtrate of A. oryzae M2040 effectively inhibited AFB1 production and A. flavus growth, suggesting A. oryzae M2040 secretes inhibitory compounds. Whole genome-based comparative analyses indicate that the A. oryzae M2040 and Afla-Guard genomes are 37.9 and 36.4 Mbp, respectively, with each genome containing ~100 lineage specific genes. Our study establishes the idea of using A. oryzae and/or its cell-free culture fermentate as a potent biocontrol agent to control A. flavus propagation and AF contamination.
Highlights
Aflatoxins (AFs) are a group of small molecular weight fungal toxins that threaten world food safety by contaminating ~25% of the world’s crops[1]
We have found that A. oryzae M2040 isolated from Korean Meju inhibits growth and aflatoxin B1 (AFB1) production by A. flavus significantly better than the widely used commercial biocontrol isolate Afla-Guard
We tested various media and found that potato dextrose broth (PDB) resulted in equal growth rates for M2040 and A. flavus, and high level production of AFB1
Summary
Aflatoxins (AFs) are a group of small molecular weight fungal toxins that threaten world food safety by contaminating ~25% of the world’s crops[1]. Of the 550,000–600,000 new liver cancer cases worldwide each year, it is estimated that 25,200–155,000 may be attributed to AF exposure[5,6] Due to their high toxicity and carcinogenicity, over 120 countries have set maximum limits of AFs in foods (4~30 ppb) and feeds (20~300 ppb)[1]. Several strategies have been developed to reduce AF contamination, including the use of a non-toxigenic strain of A. flavus to outcompete and displace toxigenic strains[17,18] This effective biological control method results in greatly reduced AF levels in a diversity of harvested agricultural products and has been applied worldwide[19,20]. We investigated the potential of using Aspergillus oryzae, the food grade non-toxigenic domesticated ecotype of A. flavus, as a biocontrol agent for inhibiting AFB1 production and growth of the toxigenic A. flavus strain NRRL 3357. This report provides a systematic investigation and strong basis for the use of the GRAS fungus A. oryzae as a potential biocontrol agent for AFB1 contamination in food, and corroborates the expired patent for using certain strains of A. oryzae and A. sojae as biocontrol agents (US6027724A)
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